I have a 1998 Silverado pickup and bought it used. Run great for the most part but just recently started missing. Heres what we have done.

1998 Silverado-350 Engine-190000 miles. 4 wheeldrive-automatic transmission.

We have a new scanner and it shows only one code P0308--#8 cyl misfire.
Truck has a bad miss in it and is getting harder to start. Used to start right off but now cranks a little longer before starting. Never fails to start though.

Recently I had a radiator hose blow and it got hot on the highway before I got it shut down. I let it cool fixed the hose and all seemed well. About a week or 2 later it started missig. I bought the scanner and heres what I've done.

We put in new plugs
new Dist Cap
new rotor
run compression test--all aroud 148 and did not leak off any.
Removed the number six plug wire and repaced it on the #8 plug and put the #8 wire on number 6 thinking it might move the miss to #six. Nope still #8 misfire.

Note: when I changed plugs the number eight plug was very wet but I have checked the new # 8 plug after about 10 miles of driving and it is looking very good. Light brown color.Still have missfire.

What do I check next???

Thanks for any input. I would love to get this truck back to the great ride it was.

I change oil and filters every 3000 miles I have had it. About 12000 miles since I bought it.

If it needs it I fix it.

Thanks agian for any input.

Dad

 

I would suspect the poppet style injectors have failed (#8). I recommend you switch them out with the new updated MFI injectors

 

This engine is not fuel injected!!

 

HI I belive that you might have Blown a head gasket or cracked a head if your spark plug was wet and had a brown color to it

 

I Have a 98 chevy 4x4 5.0 L 305 motor and I had a miss in #6 cylinder and after a bent valve in #2, I removed the head and found the crack in #6 cylinder so Everytime the motor warmed up coolant went into the exhast

 

A 1998 is fuel injected unless someone put a carburetor on it.

 

Oops I goofed--it is a 1998 Z71 Silverado if it makes a difference. I will have to look at it but I don't think it has fuel injection on it.

The wet plug was fuel not water or antifreeze. I assume from not firing properly.

Thanks for the input

Dad

 

It absoultly fuel injected. The injectors are inside the upper intake.

 

yes, it is fuel injected, guaranteed. as MDTAHOE stated, the stock injectors are problem prone, replace them with the mfi style. i did this on my 98 tahoe few months ago, big difference. easy job if you take your time and pay attention.

 

Well here is some info for everyone to hash over. First thanks for all the info and input but here is what we found out.

We were told to try a product called Seafoam. We were told that we could take the vacuum line off of the brake booster and very slowly poor half a bottle of seafoam down this hose with the motor running at an idle. Once the half bottle was in then shut the engine off and let it set for around 15 minutes. Replace the hose on the brake booster and wait.
15 minutes later we were told to start the engine and it would smoke pretty bad. It did. then we were to take it for a ride and get agreessive with the speed-(legal that is) and drive it for a few miles.
after a few miles the engine smoothed out and is now running perfect. We were told to pour the remainder of the seafoam into the fuel tank and run it through the system for further cleaning.

This was a life saver for us as we were begginning to think something serious was wrong. Our advisor told us that most people poor it in the fuel and let it work but it is best to put half the bottle directly into the engine. He saved the day for us and we now have smiles on our faces.

Hope this info helps others out as it has us. I would try it before replacing alot of expensive parts next time.

Thanks much Dad

PS: feel free to post your comments on tyhos if you have experiences with this product--good or bad.

Also I have no interest in this product and am not affilliated in any way with it or it's manufacturer.

Dad